Method and kiln for burning cement, lime, dolomite and the like



Aug. 27, 1963 E. ZELTNER 3,101,935

METHOD AND KILN FOR BURNING CEMENT, LIME, DOLOMITE AND THE LIKE FiledNov. 28. 1960 6 Sheets-Sheet 1 Fig.1

L 24 26 INVENTOR.

' ER A ZSZ'ME/Z BY zrwa mmw ATTORNEY E- ZELTNER Aug. 27, 1963 METHOD ANDKILN FOR BURNING CEMENT, LIME, DOLOMITE AND THE LIKE Filed Nov. 28. 19606- Sheets-Sheet 2 [N VEN TOR. ma/1 ZEZ/VER.

A TTORNE Y Aug. 27, 1963 E. ZELT'NER 3,101,935

METHOD AND KILN FOR BURNING CEMENT, LIME, DOLOMITE AND THE LIKE FiledNov. 28. 1960 6 Sheets-Sheet 3 I3! I30. I29 I25 I28 I27 Il9a g m 22c E-H 24 26 INVENTOR.

A TTORNEY Aug. 27, 1963v E. ZELTNER 3,101,935

METHOD AND KILN FOR BURNING CEMENT, LIME, DOLOMITE AND THE LIKE FiledNov. 28, 1960 6 Sheets-Sheet 4 123 Ill I10 l N VEN TOR. Rlc/1 ZEZiA/EIZBY wWAI/M A TTORNE Y E. ZELTNER Aug. 27, 1963 METHOD AND KILN FORBURNING CEMENT, LIME, DOLOMITE AND THE LIKE Filed Nov. 28. 1960 6Sheets-Sheet 5 Nu M WA UM 5 U .Y B

Aug. 27, 1963 ,E. ZELTNER 3,101,935

METHOD AND KILN FOR BURNING CEMENT, LIME, DOLOMITE AND THE LIKE FiledNov. 28, 1960 s Sheets-Sheet s I43 I46 I42 I44 INVENTOR. ERMA ZELfl/mzaway/{210W A TTORNE Y United States Patent Oflice 330 1335 Patented Aug.27, 1963 3,101,935 METHOD AND KILN FOR BURNING CEMENT, LIME, DOLOMTTEAND THE LIKE Erich Zeltner, Zurich, Switzerland, assignor to L. von

Roll A.G., Zurich, Switzerland, a corporation of Switzerland Filed Nov.23, 1960, Ser. No. 72,092 Claims priority, application Switzerland Dec.3, 1959 21 Claims. (Cl. 263-29) The present invention relates to a novelmethod and apparatus for burning a fiuent charge and, more specifically,to a novel method of and shaft kiln tor continuously burning cement,lime, dolomite and similar substances. The term firing as employedhereinafter is contemplated to encompass the burning, heating, annealingor sintering of the charge and generally designates a process wherein acharge is heated to a relatively high temperature with or without acorresponding change in its chemical structure.

In a shaft kiln of the type described, noncombustible hot gases areproduced by burning a suitable fuel such as coal, oil or gas in one orseveral combustion chainbers. These hot gases are then fed to thematerial or charge to be burned or sintered which is thereby heated tothe requisite firing temperature. The hot gases are the sole source ofheat for the sintering or firing process and the kiln charge is largelyprotected against the direct action of the flames and the heat ofradiation, respectively.

A shaft kiln designed to burn or sinter a charge taken from the groupshereinalbove mentioned generally comprises a vertical column such as acylinder which in turn is provided with a preheating zone, a firing orheating zone and a cooling zone. The charge or material to be sinteredis supplied from the side or from above and in the firing or heatingzone it is subjected to the action of the hot gases which are separatelysupplied to this firing or heating zone.

Arranged underneath the heating zone is a cooling zone, the fired andcooled material being removed the lower end of the vertical cylinder. Inthe cooling zone, the fired material is cooled by means of a supply ofcold fresh air supplied from below. In a firing process of the typedescribed, it is necessary, in order to achieve a good thermalefficiency, to utilize the heat obtained after the actual firing processis completed. For this purpose, the air which is heated during thecooling of the heated or fired material is either used to preheat asupply of air by means of which the hot (gases are obtained, or elsethis heated air is supplied directly to the combustion chamber for thegeneration of the hot gases. Such a method as heretofore employedprovides tor direct utilization of the thermal energy of the heatedcooling air so that the overall efliciency of the firing process is verygood. In the known processes, the hot gases which issue from the heatingzone are further employed to preheat the material or charge subsequentlyto be treated.

The above mentioned methods give rise, however, to considerabledisadvantages despite superior utilization of heat. These disadvantagesmainly arise from the use of the heated cooling air for obtaining thehot gases. In the aforesaid processes the heated cooling air is removedfrom the border area between the cooling and the heating zones by meansof the suction created by a hot-air blower. Since the heated air carriesdust, it must first be passed through a dust separator, by way ofexample a cyclone, so that such dust can be removed. The preheated fromwhich the dust has been removed subsequently passes into a blower whichsupplies it to the combustion chamber for the production of the hotgases. The removal of dust, however, entails significant disadvantagessince the cyclones are eroded by dust and require frequent replacement.Since cyclones cannot separate very small dust particles, i.e. particlessmaller than 5-10/L in size, erosion effects will still occur at the hotair blower.

In all firing or heating processes of the type described, efficientpenetration of the material lot be heated or fired by the hot gas is adecisive factor tor the throughout rate, the quality of the firedmaterial and the thermal efiiciency of the system. In the processesheretofore known, the hot gases flow directly into the preheating zoneowing to the pressure gradient so that areas exist in the heating zonewhich have been insufliciently penetrated by the hot gases. A furtherdisadvantage of the known heating processes resides in the tact that theheated cooling air is mixed with the hot gases at least locally, andthus adversely limits the heating temperature for a given hot-airtemperature. Accordingly, the temperature of the hot air must thereforebe raised a considerable extent to achieve a desired sintering orheating temperature in order to compensate for heat transfer losses tothe cooling-air.

In accordance with the present invent-ion there is provided a novelmethod of continuously burning cement, lime, dolomite and the like in 'ashaft kiln, the material to be fired or sintered being heated .to firingtemperature by hot gases which are no longer combustible and which aresupplied to the high-temperature area of the heating or firing zone. Thepresent invention is characterized by the fact that fresh-air streamsare employed for both cool-ing the treated material and for thecombustion proc ess for generating the hot gases.

The cooling air which is raised in temperature by the burnt material ispassed through a shunt duct and bypassed around the high-temperatureportion of the heating zone prior to reaching said heating zone. Theflow resistance of this shunt duct is smaller than the flow resistanceof the high-temperature Zone of the shaft. A first portion or" the hotgases employed in the process is passed through the shunt duct in orderthat the material to be fired or heated in the high-temperature portionof the heating zone may be uniformly penetrated. The warmed cooling airand the first portion of the hot gases will mix or combine with theremaining hot gases in the low-temperature portion of the heating zone,and are then collectively employed to preheat the incoming charge whichsubsequently undergoes a heat-treatment.

It may thus readily be appreciated that the warmed cooling air is used,not as combustion air for the generation of the hot gases as in mostknown methods, but for preheating .the material to be burnt.Accordingly, fresh air may be used as the air for the combustion processfor generating the hot gases employed in the sintering operation so thatno erosion effects will take place in the fresh-air duct. Removal bysuction of the heated cooling air from the shaft before it reaches theheating zone will create a comparatively low pressure region in thisheating zone so that the used hot gases will also partially be passedinto the shunt duct. The shunt duct will, therefore, influence theuniform distribution of the hot gases in the heating zone. As a result,the heating zone is uniformly penetrated by the hot gases so that thematerial is evenly burnt and with correspondingly good thermalefiiciency. At the end of the shunt duct the warmed cooling air and thefirst hot-gas portion passed into this duct will combine with the secondor remaining hot gas portion so that the collective fluid stream is nowused to preheat the material in the preheating zone of the kiln.

Accordingly, the kiln of the present invention is provided with avertical shaft in which the hot gases originating from a combustionchamber are supplied to the upper half thereof. The shaft kiln ischaracterized by the fact that a shunt duct is provided which isconnected with the shaft by means of slots or ducts the lowermost ofwhich are located below the point of supply for the hot gases, while theupper slots are located above said supply point. Since the ohargelessshunt duct provides a smaller flow resistance than the shaft filled withthe material to be burnt and with the treated material, respectively,the heated cooling air flows into the shunt duct through the lowermostslots. This air is therefore passed around the heating zone proper. Thishas the desirable effect that the heated cooling air will not reduce thetemperature of the emerging hot gases so that the required maximumtemperature of these hot gases may be kept comparatively low. A lowerpressure appears in the shunt duct than in the heating zone so that aportion of the hot gases are also partially bypassed into this shuntduct due to the suction effect. This results in a good penetration ofthe material or charge located in the heating zone by the laterallyflowing hot gases. The cooling air which is heated and passing throughthe shunt duct and said bypassed portion of the hot gases will again besupplied to the shaft through the uppermost slots or ducts and willserve, together with the rest of the hot gases, to preheat the newlysupplied material which has not yet undergone a heat treatment.

Accordingly, it is an important object of the present invention .toprovide a novel method of and a kiln for burning a charge, such ascement, lime, dolomite and the like, exhibiting superior thermalefliciency and improved firing results.

A further object of the present invention is to provide a novel methodof burning a charge, particularly suitable for firing cement, lime,dolomite and the like wherein the produced thermal energy is efiicientlyemployed and which obviates the aforementioned disadvantages.

Still another object of the present invention is the provision of anovel method of and kiln for burning a charge wherein the hot gasesemployed for heating the charge to its firing or sintering temperatureis caused to efiiciently and uniformly penetrate the charge.

Yet another object of the present invention is the provision of a methodof and apparatus for heating or firing lime, cement, dolomite and thelike'by creating such pressure conditions in the heating zone that thehot gases will uniformly and effectively penetrate the charge located insaid heating zone.

It is a further object of the present invention to provide a novelmethod of and kiln for firing a charge and the like wherein the blowersand conduits for handling the air for combustion are not subjected toerosion effects, and wherein cold, fresh air can be used for generatingthe hot gases whilst maintaining an excellent overall efiiciency for theprocess.

These and still further objects of the present invention and the entirescope of applicability thereof will become apparent from the detaileddescription given hereinafter; it should be understood, however, thatthe detailed description and specific examples, while indicatingpreferred embodiments of the invention, are given by Way of illustrationonly, since various changes and modifications within the spirit andscope of the invention will become apparent to those skilled in the artfrom this detailed description.

In the drawings wherein like reference numerals denote similar elements:

'FIGURE 1 is a vertical section of a circular shaft provided with acombustion chamber arranged above the heating zone in the axialdirection and a shunt duct embracing the high temperature portion of theheating zone;

FIGURE 2 is a vertical section of a circular shaft provided with acombustion chamber arranged outside the shaft and a core membercontaining the shunt duct arranged inside the shaft;

FIGURE 3 is a vertical section of a shaft which is rectangular incross-section and wherein the combustion chambers are arranged outsidethe shaft and provided with a core member for the supply of hot gas;

FIGURE 4 is a vertical section of a side view of the shaft according toFIGURE 3 turned by relative thereto;

FIGURE 5 is a vertical section of a shaft kiln of rectangularcross-section with a core member which contains the shunt duct; and

FIGURE 6 is a vertical section of a side view of the shaft kilnaccording to FIGURE 5 turned by 90 relative thereto.

Referring now to the drawings and, more particularly to FIGURE 1, thecylindrical shaft 10 of the kiln rests on a base member 11. The kilnbase 11 may be formed, by way of example, of four columns 12 anchored tothe floor, two of which are visible in the drawing. The columns 12support a frame member 13 which is preferably square and on which thelower end of the shaft 10 rests. Attachment of the shaft 10 to the frame13 may be effected by means of suitable supports 14. The lower end ofthe shaft 10 is closed by a revolving grate 15 which is connectedthrough the intermediary of a yoke 16 with a rotatable shaft 17. Therotatable shaft 17 is connected to a reduction gear train 18 driven by amotor 19. The material or charge treated by the action of the heat andlocated in the hollow shaft 10 is therefore broken by the revolvinggrate 15 and passes into a hopper 2t} disposed therebelow. The materialemerging from the hollow shaft 10 thus passes into the hopper 20 andsubsequently to three serially arranged valves 22a, 22b and 220. Thevalves 22a, 22b, 220 are consecutively opened by means of a linkagesystem 25a, 25b and 250, in turn actuated by a control unit 24 so thatthe burnt or fired material located in the hopper 20 will beintermittently supplied to an outlet tube 26. The valves 22a, 22b and22c are designed so as to remove the material without permitting thecooling air supplied to the shaft 10 to escape.

Connected to the hopper 20 is a supply line 27 for feeding a supply ofcooling air. The free end of the line 27 is connetced with a rotarycompressor 28, the suction side of which is connected with a filterdiagrammatically shown at 29. The rotary compressor 28 therefore sucksair through the filter 29 and supplies it, via the supply line 27 andthe hopper 20 to the lower end of the shaft 10 under a smalloverpressure. 'I his air stream, which is hereinafter referred to ascooling air, fiows through the hollow shaft 10 in an upward direction,i.e. in the direction indicated by the arrows 30 and cools the heatedmaterial flowing through the shaft 10 in the downward direction. Owingto the arrangement of the valves 22a, 22b and 220, the cooling air underpressure cannot escape through the delivery tube 26. The upper portionof the shaft 10, which is preferably cylindrical, is enclosed at apredetermined distance from its base by a jacket or sleeve 31. The outerwall 10a of the shaft 10 and the inner wall 31a of said sleeve 31 arespaced from one another to define an annular chamber 33. Owing to thefunction which this space is called upon to perform it will hereinafterbe referred to as a shunt or bypass duct. Arranged in the upper portionof the hollow shaft 10 are three rows of slots or openings, 36a, 36b and360 which connect the interior of the upper portion of the shaft 10 withthe shunt duct 33. The upper portion of the sleeve 31 is spaced from theupper edge 33a of the shaft 10 to define an opening 33b. The function ofthese slots or channels will be described in greater detail hereinafterin conjunction with the operation of the kiln.

The lower extremity or confine of the shunt duct or annular chamber 33is inclined as indicated by dotted line 37. The lowermost point of theshunt duct 33 is connected with a dust return conduit 38 which connectssaid shunt duct with two dust gates 39a and 39b. The conduit 38 and thedust gates 39a and 39b therefore enable dust which collects at the lowerend of the shunt duct 33 to pass to the valve 22a. The jacket or sleeve31 is provided with a central vertical bore 42 which accommodates atubular core or sleeve insert 43. Arranged above the core or sleeveinsert 43 is the combustion chamber 44 for the generation of the hotgases. The combustion chamber 44 is formed by an upper wall or casingmember 45 which rests on a support ring 46. This support ring 46 isretained in a desired position by a number of supporting members 47attached to the upper surface of sleeve member 31. In FIGURE 1 a singleone of these supports 47 is illustrated. The ring 46 further carries anintermediate body member 48 which embraces the outside of the core orsleeve insert 43 so as to conduct the hot gases generated in thecombustion chamber 44 into the shaft 10. The hot air duct is thereforeformed by the annular members 43, 45 and 48. The tripartite design ofthe combustion region is necessary in order to prevent the hot air ductor passageway from being destroyed due to thermal expansion. A sealingjacket 49 which is at.

least partially elastic is provided between the intermediate member 48and the core or sleeve insert 43.

The annular casing 45 forming the combustion chamber 44 is enclosed by ajacket 50 spaced from said annular casing 45. The air for the combustionprocess and for the generation of the hot gases is supplied to thisspace designated at 51 by a feed pipe or line 52. The other end of theline 52 is connected with a rotary compressor 53, the suction side ofwhich is provided with the air filter 29. The air for combustiontherefore flows through the line 52 and into the space 51 under pressureand thence passes, via an annular opening 55, into the combustionchamber 44 as indicated by the arrow 56. Arranged above the combustionchamber 44 is an oil burner diagram-, matically indicated by referencenumeral 57. The oil burns in the combustion chamber 44 when air issupplied and generates hot gases which flow into the upper portion ofthe shaft through the central core 43. The hot gases completely burn inthe combustion chamber 44 so that no combustion occurs in the interiorof the shaft 10 itself. The material or charge located in the shaft 10is therefore heated to burning or firing temperature solely by the hotgases and not by a combustion process.

Inserted in the jacket or sleeve 31 enclosing the upper shaft end 10aare several preheating tubes 60 for the supply and preheating of thecharge to be fired. Only one such preheating tube 60 is shown in FIG. 1.The upper portion of the jacket 31 and the jacket 50 are enclosed by anouter jacket 61 which opens into a discharge pipe 62. The outer jacket61 is provided with an opening at one point and is connected with acharging or stoking device as indicated at 63. The material to be firedis supplied to the charging device and is then passed into a preheatingtube 60. The hot gases previously used in the fining operation and theused cooling air flow upwardly from an upper end 60a of the preheatingtube and are passed into the discharge pipe 62 between the jacket 50 andthe outer jacket 61. This discharge pipe 62 is connected, by way ofexample, with a conventional flue known in the art.

In explaining the operation of the furnace, the kiln may be regarded asbeing composed of three zones, i.e. a preheating zone 65, a heating orfiring zone 66 and a cooling zone 67. The heating zone '66 comprises alow temperature portion 66a and a high-temperature portion 66b. Thematerial to be burnt or fired, by way of example lime, preheated in aportion of the preheating tube 60. The warmed material or chargesubsequently first passes into the low-temperature portion 66a owing toits continuous downward movement and then into the high-- temperatureportion 66b of the heating zone 66. The charge then finally moves intothe cooling zone 67 which is formed by about the lower two-thirds of theshaft 10-.

In the cooling zone 67 the material heated in the heating zone is cooledby a stream of cooling air compressed by the rotary compressor 28 andsupplied to the lower end of the shaft 10 via the line or pipe 27 andthe hopper unit 20. The cooling air then flows upward internally of theshaft 10 as indicated by the arrows 30. The cooling zone 67 ends at thelowest row of slots or channels 360. It is readily to be appreciatedthat the resistance to flow exhibited by the shunt duct 33 issubstantially smaller than the flow resistance set up by the hightemperature portion 66b of the heating zone 66 in the shaft 10 chargedwith the material to be treated. The heated cooling air will thereforenot flow through the heating zone of the shaft 10 but is bypassedthrough the slots 36c into the shunt duct 33 as indicated by the arrows30a. This clearly indicates that the heated cooling air does not passinto the high temperature portion of the heating zone but flows aroundor bypasses this zone by means of the shunt duct 33. A substantialadvantage thus obtained resides in the fact that the heated cooling aircannot reduce the temperature of the hot gases flowing out of thecombustion chamber 44. In the kiln disclosed, it will therefore besufficient if the temperature of the hot gases is only about 50 C.higher than the required maximum temperature since heat losses betweenthe hot gases and cooling air are minimized. Mention is here made of thefact that the temperature of the hot gases in those shaft kilns in whichthe heated cooling air mixes with the hot gases must be above thedesired heat treating temperature at an extent substantially exceedingC.

The above description clearly points out that'the pressure in theannular shunt duct 33 is substantially the pressure set up in theinterior of the high temperature portion 66b of the shaft 10. One of theeffects thereof is that the hot gases flowing downward from the centraltube 43 at least partially tends to pass into the annular shunt duct 33by virtue of the pressure gradient. The rows of slots 36a and 36b areprovided for the hot gases. The hot gases therefore flow radiallyoutward from the lower end of the central core or sleeve insert 43 andenter the annular shunt duct 33 through the rows of slots 36a and 3612.This results in the feature that the material to be heated or burnt inthe high-temperature zone 66b of the heating zone 66 will be uniformlypenetrated as indicated by the arrows 70. The upper end of the shuntduct 33 is provided with an annular slot 33a through which the heatedcooling air and the portion of the hot gas which has passed into theshunt duct 33 through the slots 36a and 36b are again supplied to thelow temperature portion 66a of the burning zone 66. There the air andthe gas originating from the shunt duct 33 will mix with the hot gaswhich has passed into the lowtemperatu-re portion 66a of the burningzone 66 directly from the high-temperature portion 66b, as indicated bythe arrow 71. All the gas and all the heated cooling air forming acollective heated fluid mix-ture will then flow through the preheatingtube 60 in the upwand direction and pass into the flue 62 as indicatedby the arrows 73. When passing through the preheating tube 60 the gasesand the heated cooling air, respectively, transfer their heat to thematerial to be burnt located in the respective preheating tube 60. Theair-gas mixture or heated fluid mixture formed above the annular slot33a generally will still have a temperature somewhat above the minimumburning temperature of the charge so that a burning or heating processwill already be performed to a limited extent in the lower portion ofthe respective preheating tube 60. The drawing shows that thelowtemperature portion 661: of (the heating or burning zone 66 extendsas far as the lower end of the preheating tube 69. The gases leaving theupper end 60a of the respective preheating tube 60 have transferredpractically their entire heat to the incoming material to be burnt whichhas been newly supplied so that the kiln will operate under very goodconditions of thermal efficiency.

The burnt material passes, as has already been outlined, continuouslydownward in the shaft and it is disintegrated into individual pieces bythe revolving grate disposed at the lower end of said shaft 10.Subsequently, the cooled material passes through the valves 22a, 22b and220 to the outlet or delivery tube 26. It will be seen that the shaftkiln disclosed combines a number of substantial advantages. In the firstplace, fresh air is employed for the combustion process for thegeneration of the hot gases so that it will not be necessary to purifythe warmed cooling The use of fresh air for the combustion process willeliminate all erosion eflfects in the compressor 53 and in the fresh airconduit or line 52. A particular noteworthy advantage is secured byemploying the shunt duct 33. This shunt duct 33 has, on the one hand,the effect that the heated cooling air will not pass into thehigh-temperature portion 66b of the burning zone 66 and, on the other,that the hot gases will uniformly penetrate the material located in theheating or burning zone 66 owing to the resulting pressure gradient.This uniform penetration increases the quality of the material, thethroughput rate, and consequently the thermal efiiciency. In addition,the shaft kiln disclosed enables the heat to be practically completelyutilized since the gas-air mixture obtained will almost entirelytransfer its heat to the incoming material not yet burnt which is newlysupplied.

The shaft kiln shown in FIG. 2 differs from the shaft kiln according toFIG. 1 in that the hot gases are radially supplied from the outside ofthe shaft while the shunt duct is located centrally in the upper shaftportion. The kiln base, the revolving grate, the arrangement of valvesand the rotary compressors in this embodiment according to 'FIG. 2 aresimilar to those members in FIG. 1, like reference numerals generallyindicating similar structure, so that for the sake of clarity a furtherdescription may be dispensed with.

The combustion chamber here designated at 84 is formed by a casing 81rigidly connected with the shaft 82. The casing member 81 of L-shapedcross-section has its lower end resting on a supporting structure 83which in turn rests on a projection or table portion 84 of the kilnbase. The casing 81 forming the combustion chamber 80 is again enclosedby a jacket member 85 connected with an air supply line 52. The oilburner supplying the fuel for the combustion process anddiagrammatically indicated at 86 is located at the lower end of thecombustion chamber 86 The combustion air circulating within the jacket85 flows into the combustion chamber 80 in the region of the burneropening, as indicated by the arrows 87. The combustion chamber 80 opensinto a sleeve member or the like providing an annular chamber 88enclosing the shaft 82, said chamber 88 communicating with the interiorof the shaft via slots or ducts 89. In the present embodiment the hotgases emanating from the combustion chamber 80 therefore pass radiallyinto the interior of the shaft 82 from eX- ternally thereof.

Arranged across the upper end of the shaft 82 is a support 90 carrying asleeve or core insert 92 by means of a suspension bar 91, the sleeveinsert 92 is located at the center of the shaft 82 and terminatessomewhat short of the middle of said shaft 82. The lower end of thehollow sleeve insert 92 is open and is provided with an openingdesignated by the reference numeral 93 forming the shunt duct. The shuntduct 93 is connected with the interior of the shaft 82 by a lower row ofslots 94 arranged below the hot gas inlet slots or channels 89 and by asecond row of slots or channels 95 located above the hot gas slots 89.Arranged above the shaft 82 is :a hood member 96 which conducts thegases issuing from the shaft into a flue 97. The hood member 96 furthersupports a charging device for the material to be burnt as indicated at97a,

The kiln according to FIG. 2 may be subdivided into separate zones in amanner similar to the kiln shown in FIG. 1. The different zones beingdesignated by the same reference numerals as in FIG. 1, towit, thepreheating zone is indicated at 65, the burning zone at 66 and thecooling zone at 67, said burning zone again comprising ahigh-temperature region 6611 and a low-temperature region 66a. Coolingair flows into the shaft 82 through the cool air conduit againdesignated by reference numeral 27 and cools the burnt material locatedin the lower portion of the shaft 82. As indicated by the arrows 98, thecooling air passes into the shunt duct 93 through the lower opening andthe slot 93a since said shunt duct 93 presents a region of less flowresistance than the shaft 32 filled with the material to be burnt. Inthe same manner as in the embodiment according to FIG. 1, the preheatedcooling air cannot establish contact with the hot gases entering theshaft 82 through the hot-gas inlet openings 39. The pressure set up inthe shunt duct 93 is therefore lower than that appearing in the shaft 32at the corresponding elevation. One of the consequences of this pressuregradient is that a portion of the hot gases entering through theopenings 89 passes into the shunt duct 93 through the slots 94 asillustrated by the arrows 99. One effect thereof is that the hot gasuniformly penetrates the high-temperature portion 66b of the heatingzone 66 resulting in the advantages recited in conjunction with thedescription of FIG. 1. The cooling air-gas mixture supplied to the shuntduct 93 emerges from this duct through the row of slots 95 and againpasses into the low-temperature portion 66a of the shaft 82. The air-gasmixture there mixes with the remaining portion of the hot gases whichhave not passed into the shunt duct 93, the direction of flow of whichis indicated by the arrows 160. The entire air-gas mixture or fluidstream then flows through the low-temperature portion 66a into thepreheating zone 65 and heats the incoming material to be burnt.

The shaft kiln according to FIG. 2 operates in the same manner as thatshown in FIG. 1 and combines the same advantages. The essentialdifference between the two embodiments, as previously stated, consistsin that the shunt duct of the shaft kiln according to FIG. 1 is locatedon the outside and the burning chamber coaxially with the axis of thekiln, while the shunt duct in the embodiment according to FIG. 2 islocated inside of the shaft and the burning chamber laterally thereof.

FIGS. 3 and 4 show a further kiln arrangement which is of rectangularcross-section in distinction to the kilns shown in FIGS. 1 and 2, thehot gases of combustion egain flowing from the inside to the out-side asexplained in conjunction with FIG. 1. FIG. 3 is a longitudinal sectionof the smaller cross-sectional area, and FIG. 4 is a view, partly insection of the kiln seen from its larger side. The kiln base, the aircompressors and the arrangement of valves are again identical with thecorresponding members illustrated in FIG. 1 so that repetition of thedescription is herein dispensed with, like reference numerals generallyindicating similar structure.

In the kiln according to FIGS. 3 and 4, the revolving grate of FIGURE 1is replaced by a cylinder grate 102. The individual cylinders of saidgrate 102 are driven by a motor 105 via gearing means 103. The functionof the grate 102 is the same as that of the revolving grate illustratedin the preceding embodiments. As may clearly be seen from FIG. 4, twoopposite or diametrically opposed supports 1% are arranged on the kilnbase ill, each of which carries a platform or table 108 via the struts107. The platforms in turn carrying a casing member 110 provided with acombustion chamber or compartment 111. The oil burners 112 are arrangedat the outer ends of the casing members lit). The casing members 110 areeach encircled by a jacket 113, the air for combustion being supplied tothe space formed by the jacket 113 and the associated casing 1:10 vialine 52 and branch lines 27a and 27b. The combustion air cornbines withthe oil supplied from the oil burners 112 and provides the necessary hotair required [for the combustion process taking place in the respectivecombustion compartments 111.

The two combustion chambers 111 are interconnected by a hot-gas channelor passageway 120 which is located in an internally arranged sleeveinsert or core piece 121. This sleeve or core piece 121 extends, asclearly shown by FIG. 3, through the kiln in the longitudinal directionand separates the interior of the shaft into two sections convenientlydesignated by reference numerals 119a and 11%. The interconnectingchannel 120 is connected with the interior of the shaft 127 by two rowsor banks of slots or channels 123 and 124. The hot gases flowing fromthe combustion chambers 111 into the hot-air channel 120 from oppositesides thus reach the interior of the shaft through the upper and lowerslots 123 and 124.

As can further clearly be seen in FIG. 3, two substantially flat jacketor sleeve members 125 are arranged at the larger side surfaces of theshaft and are located at a predetermined distance from the side walls127 of the shaft and each form an intermediate space or duct 128. Thejacket members or sleeves 125 are connected with the shaft body and,respectively, the side walls 127 by means of yokes 125a arranged at theupper ends. The two intermediate spaces 128 each constitute a shuntduct. The two shunt ducts 128 communicate with the interior of the kilnvia three rows of slots or channels 129, 130 and 131. The two lower rowsof the slots or channels 129 and 13 are located below the inlet openings123 and 124 for the hot gases while the upper row of slots 131 isarranged above said inlet openings for the hot gases.

The two lower ends of the shunt ducts 128 are connected with a dust gatevia conduit lines 132, which dust gate is identically designed similarto the dust gate 39a, 39b of the shaft kiln shown in FIG. 1. In \FIG. 4part of the jacket or sleeve member 125, the kiln wall 127 and part ofthe core member .121 have been shown so that the rows of slots 129, 131)and 131, and a portion of the inside of the hot-gas channel 120 areclearly visible. The upper end of the shaft is closed by a flue13'3'which also contains a charging device 134 as best seen in FIGS. 3and 4.

In operation, a quantity of cooling air is supplied from the lower endof the shaft via conduit 27. This cooling air flows into the shunt ducts128 through the slots 12 9. In a manner similar to that of the twoembodiments previously described, the lowest row of slots defines theupper region of the cooling zone 67. At the same time, the underpressurein the shunt ducts 128 draws the hot gas emerging preferably from thelower hot-gas openings 124 into the shunt ducts 128 so that the materialto be heated or fired is fully penetrated by the hot gas in thehigh-temperature portion 66b of the heating zone 66. A portion of thehot gases flow into the shunt ducts 128 through the intermediate row ofslots 130. The gas-air mixture located in the shunt ducts 128 returnsback into the shaft through the upper row of slots 131. The temperatureof the thus formed fluid mixture is still above the burning temperatureof the material, so that it causes a heating process to occur in thelow-temperature portion 66a of the heating zone 66. On the dischargeside of the slots 131 the gas-air mixture coming from the shunt ducts128 mixes with the remaining hot-air portion which has not reached theshunt ducts 128 mainly emerging from the upper row of hot gas openings 123. The fluid mixture of hot gases and cooling air then rises upwards inthe shaft and permeates, as previously stated, the lowtemperatureportion 66a of the heating zone 66 and then the preheating zone 65'.

It may be seen that the shaft kiln according to FIGS. 3 and 4 achievesthe same advantages as obtained by the shaft kilns previously describedwith respect to the other embodiments. What is remarkable in theshaftkiln according to FIGS. 3 and 4 is the rectangular cross-section ofthe shaft and the supply of hot gases through the core member 121. Thehot-gas channel in the core member 121 is provided, as alreadydescribed, with two rows of slots 12:3 and 124. Thegas emerging from therow of slots 124 flowing mainly into the shunt ducts 128 while the gasissuing from the row of slots 123 remains largely in the interior of theshaft. The cross-section described requires the presence of two shuntducts which, however, perform the same function as the individual shuntducts in the shaft kilns according to FIGS. 1 and 2.

FIGS. 5 and 6 show a further embodiment of a shaft kiln having arectangular cross-section. In FIG. 5 there is shown a longitudinalsection of the smaller cross-sectional area and FIG. 6 a view of alarger side surface of the shaft partly in section. The design andarrangement of the kiln base, the valves and the compressors is the sameas in the embodiment according to FIGS. 3 and 4 while the burner isdesigned similarly to that in the shaft kiln according to FIG. 2 likereference numerals again denoting similar structure. Provided at thelarger side walls of the rectangular shaft are sleeve means or the likeproviding two hot-gas channels 141 which are connected with thecombustion chamber 142. The two channels 1141 are connected with theinterior of the shaft via two rows of openings or slots 143 and 144through which the hotgases enter the interior of said shaft. Arrangedparallel with the side walls 140 of the shaft and internally thereof isa sleeve insert or core piece 146 provided with an extended slottedopening 147. This opening 147 constitutes the shunt duct. As best seenin FIG. 6, the lower boundary surface 147a of the shunt duct isinclined. This lower surface 147a communicates with a dust return line148 which is connected with a two-stage dust gate 149 similar to thedust gates 39a, 39b of FIGURE 1. The shunt duct is connected with thetwo shaft halves separated by the core piece 146 via three rows of slotsor openings 150, 151 and 152. The two lower rows of slots and 1531 arelocated below the hot-gas supply openings 143 and 144 while the upperrow of slots 152 is arranged above said hot-gas openings. Arranged abovethe upper shaft end is a hood member which establishes communicationwith a conventional flue. A charging device 161 is again located withinsaid hood 160.

The shaft kiln according to FIGS. 5 and 6 operates in the same manner asexplained in conjunction with the previous embodiments. The cooling airentering from below transver-ses the cooling zone 67 and passes into theshunt duct 147 through the rows of slots 150. In the same manner, thehot gases of the two rows of lower hot-gas supply openings 144- passinto the shunt duct 147 through the rows of slots 151. This enables thematerial to be heated to be thoroughly penetrated by the hot gases inthe heating zone. The cooling air which has now been raised intemperature and the hot gases appearing in the shunt duct 147 thenceflow back through the upper slots 152 into the upper shaft halves 153aand 15317. Where the slots 152 open, the air-gas mixture appearing inthe shunt duct 147 now combines with the remaining hot-gas portion thathas not been passed through the shunt duct 147 and which emanates mainlyfrom the upper row of openings 143. The gas-air or fluid mixture willthen flow through the low temperature portion 66b of the heating zone 66in an upward direction and heats the incoming material next to betreated. The shunt duct 147 therefore performs the same function as inthe shaft kilns hereinabove described. On the one hand, the heatedcooling air is bypassed about at least the high-temperature portion 66bof the heating zone 66 so that this heated cooling air cannot reduce thetemperature of the hot gases. It is to be appreciated that this featureof the shaft kilns described makes it sufficient for the hot gases tohave a temperature which is only 50 C. higher than the desired maximumheating temperature. The shunt duct 147 further causes a pressuregradient in the shaft, which pressure gradient has the advantageouseffect that the hot gases uniformly penetrate all of the material to beheat treated. With respect to all the embodiments of the shaft kilnsdisclosed, it may be said that they provide a high throughput rate, goodthermal efficiency with a minimum possibility of breakdown. The shaftkilns thus meet all the requirements necessary for efiicient practicaloperation. A numher of modifications of the embodiments shown arepossible. In particular, after-burners may be provided in the shuntducts which will contribute to heating the ases and the heated coolingair, respectively, and may result in a further improvement of thethermal etficiency. in FIG- URE 1 such an after-burner or burner means2% is provided in the region of the shunt duct 33 for introducing asuitable fuel to further heat the bypassed cooling air and gases. Itshould be understood that a substantially similar arrangement can beprovided for the corresponding shunt ducts of the other herein describedembodiments. Although the present invention has been described inconjunction with a charge such as cement, lime, dolomite or the like,the same have been given by way of illustration only as other chargesmay equally well be employed.

Having thus described the present invention what is desired to besecured by United States Letters Patent is:

'1. A method of heat treating a charge such as cement, lime, dolomiteand the like, comprising the steps of mixing a quantity of air with afuel and burning the same to complete combustion to produce hot gases,directing said hot gases with substantially symmetrical infeed into contact with a charge to be heat treated in a heating section of a kiln,distributing said hot gases into substantially at least two hot gasstreams, each of which is operable throughout approximately one-half ofthe cross-section of said kiln to thus uniformly penetrate and heattreat the charge located therein, bypassing a first portion of said hotgases into a duct which does not contain said charge while the remainingmajor portion of said hot gases freely circulates through said chargefor heat treating thereof, feeding a supply of cooling air through acooling section of said kiln to contact said charge for heat transfertherewith and toward said hot gases circulating through said charge,then bypassing said cooling air into said duct which does not containsaid charge adjacent the upper region of said cooling section at leastprior to intimate contact of said cooling air with said hot gases toprevent heat transfer between said cooling air and said hot gases tothereby prevent undesired reduction of the temperature of said hot gasesin contact with said charge, said bypassed cooling air and said firstportion of said hot gases freely mixing IVitllifl said duct, thencommingling said bypassed cooling air and said first and remaining hotgas portions to produce a fluid mixture of hot gases and air, thencausing said fluid mixture to circulate through another portion of acharge in a preheating section of said kiln to raise the temperature ofthe same in preparedness for a similar heat treating operation.

2. A method or" heat treating a charge such as cement, lime, dolomiteand the like, comprising the steps of mixing a quantity of air with afuel and burning the same to com plete combustion to a temperature rangeexceeding the desired heat treating temperature for the charge byapproximately 50 degrees to produce hot gases, directing said hot gaseswith substantially symmetrical infeed into contact with a charge to beheat treated in a heating section of a kiln, distributing said hot gasesinto substantially at least two gas streams, each of which is operablethroughout approximately one-half of the cross-section of said kiln tothus uniformly penetrate and heat treat the charge located therein,bypassing a first portion of said hot gases into a duct which does notcontain said charge while the remaining major portion of said hot gasesfreely circulates through said charge for heat treating thereof, feedinga supply of cooling air through a cooling section of said kiln tocontact said charge for heat transfer therewith and toward said hotgases circulating through said charge, then bypassing said cooling airadjacent the upper region of said cooling section into said duct whichdoes not contain said charge immediately prior to intimate contact ofsaid cooling air with said hot gases to prevent heat transfer in saidheating section between said cooling air and said hot gases to therebyprevent undesired reduction of the temperature of said hot gases incontact with said charge, said bypassed cooling air and said firstportion of said hot gases freely mixing within said duct, thencommingling said bypassed cooling air and said first and remaining hotgas portions to produce a fiuid mixture of hot gases and air, thencausing said fluid mixture to circulate through another portion of acharge located in a preheating section of said kiln to raise thetemperature of the charge in preparedness for a similar heat treatingoperation.

3. A method of heat treating a charge such as cement, lime, dolomite andthe like, comprising the steps of mixing a quantity of air with a fueland burning the same to complete combustion to produce hot gases,directing said hot gases with substantially symmetrical infeed intocontact with a charge to be heat treated in a heating section of a kiln,distributing said hot gases into substantially at least two hot gasstreams, each of which is operable throughout approximately one-half ofthe cross-section of said kiln to thus uniformly penetrate and heattreat the charge located therein, bypassing a first portion of said hotgases into a duct which does not contain said charge while the remainingmajor portion of said hot gases freely circulates through said chargefor heat treating thereof, feeding a supply of cooling air through acooling section of said kiln for contact with said charge for heattransfer therewith and toward said hot gases circulating through saidcharge, then bypassing said cooling air from adjacent the upper regionof said cooling section into said duct which does not contain saidcharge at least prior to intimate contact of said cooling air with saidhot gases to prevent heat transfer between said cooling air and said hotgases in said heating section to thereby prevent undesired reduction ofthe temperature of said hot gases in contact with said charge, saidbypassed cooling air and said first portion of said hot gases freelymixing within said duct, said cooling air when disposed in said ductaiding to produce a pressure differential between said heating sectionof said kiln and said duct to facilitate bypass of said first portion ofsaid hot gases, then commingling said bypassed cooling air and saidfirst and remaining hot gas portions to produce a fluid mixture of hotgases and air, then causing said fluid mixture to circulate throughanother portion of a charge disposal in a preheating section of saidkiln to raise the temperature of the charge in preparedness for asimilar heat treating operation.

4. A method of heat treating a charge such as cement, iime, dolomite andthe like in a kiln provided with a shunt duct, said kiln including aheating section, a cooling section and a preheating section; comprisingthe steps of mixing a quantity of air with a fuel and burning the sameto complete combustion to produce hot gases, directing said hot gaseswith substantially symmetrical infeed into contact with a charge to beheat treated in said heating section of the kiln, distributing said hotgases into substantially at least two hot gas streams, each of which isoperable throughout approximately one-half of the cross-section of saidkiln to thus uniformly penetrate and heat treat the charge locatedtherein, bypassing a first portion of said hot gases into said shuntduct which does not contain said charge while the remaining majorportion of said hot gases freely circulates through said charge for heattreating thereof, feeding a supply of cooling air through thepredominant portion of said cooling section of said kiln and said chargefor heat transfer therewith and toward said hot gases circulating insaid heating section, then bypassing said cooling air into said shuntduct which does not contain said charge prior to intimate contact ofsaid cooling air with said hot gases to prevent heat transfer betweensaid cooling air and said hot gases to thereby prevent undesiredreduction of the temperature of said hot gases in contact with saidcharge, said bypassed cooling air and said first portion of said hotgases freely mixing within said shunt duct, then comminglinglsaidbypassed cooling air and said first and remaining hot gas portions toproduce a fluid mixture of hot gases and air, and finally causing saidfluid mixture to circulate through another portion of a charge locatedinfsaid preheating section of said kiln to raise the temperature of thesame in preparedness for a similar heat treating operation.

5.'A method ofheat treating a charge according to claim 4, including thestep of introducing a fuel into said I shunt duct to further heat saidbypassed cooling air and said"first' portiono'f sai'dhot gases freelymixing within said shunt duct to raise the temperature thereof. v

6'. A kiln for heat treating a change, comprising a shaft having ahollow interior defined by side walls, said kiln being successively,provided with apreheating section, a heating section and a coolingsection withat least said heating section and said cooling sectionlocated within said hollow interior of said shaft, charging meanscooperable with said shaft for feeding a charge to be heat a pair ofseparate diametrically opposed combustion chamibers cooperating withsaid separate compartments.

v 9. A kiln for heating treating a charge, comprising a shaft providedwitha hollow interior defined by sidewalls and having a longitudinalaxis, said kiln being successively provided with a preheating section, aheating section and a cooling section with at least said heating sectionand said cooling section located said hollow interior of said shaft,charging means cooperable with said shaft for feeding a charge to beheat treated to said hollow interior of said shaft, combustion meanscoaxially arranged with respect to said longitudinal axis of said shaftin registry with said heating section of said shaft for directing asupply of hot gases with symmetrical infeed thereto for contact withsaid change, feed means for supplying a respective quantity of air tosaid combustion means and said cooling section of said shaft, and'ahollow sleeve member disposed adjacent one end of said shaft at least inthe treated to'said hollow interior of said shaft, combustion section ofsaid shaft, a member arranged in said hollow :interior of said shaft, amember arranged outside of said shaft adjacent the side' walls thereofand in the region side wall of saidjhea'ting section of said shaft'intheregion means 'comrnunicating'with said hollow interior of said ofsaid heating section of said kiln, said interiorly arranged member beingprovided opening means com- 'municating with said hollow interior "ofsaid shaft, said of said outside arranged member being provided withslot j sha ftsaid interiorly arranged member, one of c said memb slbein-g in registry 'wi-th said combustion means with"the' other of saidmembers defining a shunt duct, thereby penmitting bypassing of at leasta portion of said hot gases into said shunt duct prior to moving throughthe' predominant portion of said heating section as well as removingsaid cooling air prior) to intimate mixing and circulation thereof witha remaining portion of c said hot gases located in said heating sectionof said kiln.

kiln for heat treating a charge, comprising a shaft havingal'hollowinteriordefined by side walls, said kiln being successivelyprovided with' a preheating} section, a.

heating section'and a 'coolingsection with at least said heating sectionand said cooling section located within said hollow interior of saidshaft, charging means cooperable with said shaft, for feeding a chargeto be heat treated to said hollow interior of said shaft, combustionmeans in registry with said heating section of said shaft for directinga supply of hot gases thereto for contact with said charge,- feed meansfor supplying a respective quantity of air to said combustion means andsaid cooling section of said shaft, and a hollow sleeve member disposedadjacent one end of said shaft at least in the regionof said heatingsection and spaced from the outer wall of said side wall to. definetherewith a shunt duct, said side wall of said shaft opposite saidhollow sleeve member being provided with slot means communicating saidheating section of said hollow interior of said shaft with said shuntduct, .to thereby permit bypassing of at least aportion of said hotgases in-to said shunt ductprior to moving throughout said heatingsection as well as removing said cooling air into said shunt duct priorto intimate mixing and circulation thereof with a remaining portion ofsaid hot gases located in said heating section of said kiln.

8. A kiln, for heat treating a charge according to claim 7, furtherincluding a sleeve insert mounted internally of said shaft in alongitudinal direction to divide said holregion of said heating sectionand spaced from the outer wall of said side wall to define a shunt duct,said side wall of said shaft opposite said hollow sleeve member beingprovided with slot'means communicating said hollow interiorof saidshaftthe regionI-of said heating section with said shunt duct, totherebypermit bypassing of at least a portion of said hot gasesint'osaid shunt duct prior to moving throughout said-heating section as wellas removing said cooling air into said shunt duct prior to intimatemixing and circulation thereof with a remaining portion of said hotgases located in said heating section of said kiln. s

10. A method of treating a charge such as cement,

lime, dolomite and the like, comprising the steps of mixing a quantityof air'with a fuel and burning the same to produce hot gases, directing.said hot gases into contact with a change to be heat treated a heatingsection of a kiln, distributing said hot gases through said heatingsection of said kilninto at least two hot gas streams, each of which iseffectively operative throughout approximately one-half the crosssectional area of said heating section of said kiln, forming a pressuregradient between said heating section and a'region'devoid of saidcharge, with said charge. devoid region defining a shunt duct possessinga flow resistance which is smaller than that of said charge-containingheating section, said formed pressure gradient causing bypass of aportion cf said hot gases into said shunt duct while the remaining majorportion of said hot gases passes through said charge located in saidheating section, feeding a" supply of cooling 'air through said chargedisposed in a cooling section of said kiln for heat transfer therewith.and toward said hot gases in contact with said charge and flowingthrough said heating section, then bypassing said cooling air into saidshunt duct which does not contain said charge prior to intimate contactof said cooling air with said hot gases in contact with said charge, toprevent heat transfer between said cooling air and said hot gases insaid heating section in contact with said charge, thereby preventing anundesired reduction of the temperature of said hot ing at leastsubstantially centrally within said charge,

forming a pressure gradient between said heating section and a regiondevoid of said charge, with said charge devoid region defining a shuntduct which possesses a smaller flow resistance than that of saidcharge-containing heating section of said kiln, said pressure gradientcausing bypass of a portion of said hot gases into said shunt duct whilethe remaining major portion of said hot gases pass through said chargewithin said heating section, feeding a supply of cooling air throughsaid. charge disposed in a cooling section of said kiln for heattransfer therewith and toward said hot gases flowing through saidheating section in contact with said change, then bypassing said coolingair from adjacent the upper region 9f said cooling section into saidshunt duct immediately prior to intimate contact of said cooling airwith said hot gases in contact with said charge to prevent heat transferbetween said cooling air and said hot gases in said heating section,thereby preventing an undesired reduction of the temperature of said hotgases in contact with said charge.

12. A kiln for heat treating a charge according ito claim 7, whereinsaid hollow sleeve member is spac'ie'd from an upper edge of saidshaftto define an openihg permitting communication of said shunt duet withsaid preheating section of said kiln, said preheating section beingdefined by at least one preheating tube supported by said hollow sleevemember and extending toward said opening. I

13. A kiln for heat treating a charge according to claim 7, wherein said:Sldfi walls of said shaft define a circular cross-section, and saidshunt duct is annular:

14. A kiln for heat treating a charge according to claim 13, whereindust removal means are provided which cooperate with the lower extremityof said shunt duct to remove impurities contained therein.

15. A kiln for heat treating a charge, comprising a vertical shafthaving a hollow interior defined by .wall portions and adapted toreceive a charge therein, sleeve means supported by an upper portion ofsaid vertical shaft and disposed adjacent the outer surface thereof andspaced therefrom to define a shunt duct, said kiln being successivelyprovided with a preheating section, a heating section and a coolingsection with at least said heating section and said cooling sectionbeing located within said hollow interior of said vertical shaft,charging means cooperable with said vertical shaft for feeding a chargeto be heat treated to said hollow interior of said vertical shaft,combustion means adjacent said upper portion of said vertical shaft inregistry with said heating section and coaxially arranged with respectto the longitudinal axis of said shaft for directing a supply of hotgases into contact with said charge, feed means for supplying arespective quantity of air to said combustion means and said coolingsection of said vertical shaft, said Wall portion of said vertical shaftbeing provided :with openings in the region of said heating sectionpermitting bypass of at least a portion of said hot gases into saidshunt duct prior to moving throughout said heating section as well asremoving said cooling air into said shunt duct to prevent intimatemixing and circulation of said cooling air with a remaining portion .ofsaid hot gases located in said heating section of said kiln.

16. A kiln for heat treating a charge according to claim 6; wherein saidother member defining a shunt duct is said interiorly arranged memberand comprises a sleeve insert which is disposed in said hollow interiorof said shaft at least in the region of said heating section.

17. A kiln according to claim 16; wherein said sleeve insert issupported by an upper portion of said shaft.

18. A kiln for heat treating a charge according to claim 16; whereinsaid sleeve insert is mounted internally of said shaft and extended in alongitudinal direction to divide said hollow interior into twoseparatecompartments.

19. A kiln (for heat treating a charge according to claim 18; whereinsaid combustion means communicates with said two separate compartmentsto supply hot gases thereto.

20. A kiln for-heat treating a charge according to claim 16; wherein atleast one portion of said opening means of said internally arrangedsleeve insert is arranged adjacent the lower extremity of said heatingsection and at least one other portion of said opening means beingarranged adjacent the upper extremity of said heating section to permitbypass of at least a portion of said hot gases and said cooling airaround saidheating section of said kiln. I I

21. A kiln for heat treating a charge according to claim 6; wherein saidother member defining a shunt duct is said outside arranged member andcomprises sleeve means supported by an upper portion of said shaft inspaced relation (from said side walls to provide said shunt duct, saidone member which is inregistry with said combustion means being aninsert member located in said shaft to divide the latter into separatecompartments.

ReferencesCitedin the file of this patent UNITED STATES PATENTS1,895,284 Hay. Jan. 24,193 2,744,743 .Beggs et a1. May 8,1956 2,788,961Pooley et al Apr. 16, 1957 2,960,323 Ludin Nov. 15,-1960 2,996,292Grafet al. Aug. 15, 1961

1. A METHOD OF HEAT TREATING A CHARGE SUCH AS CEMENT, LIME, DOLOMITE ANDTHE LIKE, COMPRISING THE STEPS OF MIXING A QUANTITY OF AIR WITH A FUELAND BURNING THE SAME TO COMPLETE COMBUSTION TO PRODUCE HOT GASES,DIRECTING SAID HOT GASES WITH SUBSTANTIALLY SYMMETRICAL INFEED INTOCONTACT WITH A CHARGE TO BE HEAT TREATED IN A HEATING SECTION OF A KILN,DISTRIBUTING SAID HOT GASES INTO SUBSTANTIALLY AT LEAST TWO HOT GASSTREAMS, EACH OF WHICH IS OPERABLE THROUGHOUT APPROXIMATELY ONE-HALF OFTHE CROSS-SECTION OF SAID KILN TO THUS UNIFORMLY PENETRATE AND HEATTREAT THE CHARGE LOCATED THEREIN, BYPASSING A FIRST PORTION OF SAID HOTGASES INTO A DUCT WHICH DOES NOT CONTAIN SAID CHARGE WHILE THE REMAININGMAJOR PORTION OF SAID HOT GASES FREELY CIRCULATES THROUGH SAID CHARGEFOR HEAT TREATING THEREOF, FEEDING A SUPPLY OF COOLING AIR THROUGH ACOOLING SECTION OF SAID KILN TO CONTACT SAID CHARGE FFOR HEAT TRANSFERTHEREWITH AND TOWARD SAID HOT GASES CIRCULATING THROUGH SAID CHARGE,THEN BYPASSING SAID COOLING AIR INTO SAID DUCT WHICH DOES NOT CONTAINSAID CHARGE ADJACENT THE UPPER REGION OF SAID COOLING SECTION AT LEASTPRIOR TO INTIMATE CONTACT OF SAID COOLING AIR WITH SAID HOT GASES TOPREVENT HEAT TRANSFER BETWEEN SAID COOLING AIR AND SAID HOT GASES